This invention relates to an improved system for supplying air to the aeration chamber of an aerobic wastewater treatment plant.
In remote areas, newly developed subdivisions, or other locations where a municipal sewer system is not available, small anaerobic or aerobic wastewater treatment plants are used to handle the wastewater produced. Septic tanks use anaerobic bacteria to convert the organic solid waste in the wastewater stream. Usually, however, most of the organic solids settle as sludge to the bottom of the septic tank and must be pumped out periodically.
Aerobic wastewater treatment plants use “extended aeration” to efficiently encourage aerobic bacteria growth. Extended aeration includes contacting the wastewater with a large number of small bubbles of oxygen-carrying gas, thus maximizing the surface area for oxygen transfer. Air or oxygen is generally pumped into the tank through diffusers that break up the air into thousands of tiny air bubbles. Aerobic bacteria in the water convert waste products to water and CO2, thus purifying the water and reducing the wastewater to a clear odorless liquid. Through extended aeration, the home wastewater treatment plants accelerates the reduction of waste substantially beyond the rate of reduction which can be accomplished with an anaerobic septic tank or even the rate of reduction observed in nature.
One problem associated with aerobic wastewater treatment plants is the failure of the flow of air in the aeration chamber to keep some of the solids from continuously settling to the bottom, where they build up a layer of sludge in the aeration and clarifier chamber, requiring periodic removal. It is desirable that a minimum of sludge removal be required since, in addition to the high maintenance requirement, disposal of the sludge presents an ecological problem. An accumulation of sludge within the unit further results in a deterioration of the wastewater treatment process because the high concentration of bacteria in the sludge rapidly consumes the available oxygen in the immediately surrounding water, whereupon, the bacteria begins to break down nitrogen compounds in the sludge to release bonded oxygen. This results in a release of nitrogen gas, which rises to the surface producing scum and disrupting the bacterial conversion. Thus, bacteria and waste need be maintained in solution for optimum conversion.
The basic aerobic wastewater treatment plant for home use includes a tank which is buried in the ground except for the top opening which provides access to the inside of the tank. The tank is divided into an aeration chamber into which the wastewater flows, where oxygen is supplied to cause aerobic bacteria to digest the solids in the wastewater, and a clarifier chamber from which the treated wastewater exits the treatment plant. An external oxygen source is generally connected to a PVC line which drops through the top portion of the tank to the bottom of the tank in the aeration chamber.
There are two basic designs of these treatment plants known in the art which are devised to retain solids in the aeration chamber until they can be broken down by bacteria. The first design includes two substantially rectangular chambers separated by a baffle or partition extending from the top of the plant a substantial length down through the plant. Wastewater must flow under this baffle to reach the clarifier chamber. A deflector directing errant solids out of the clarifier chamber back into the aeration chamber is a frequent element in this type of plant.
The second basic design of treatment plants includes a partition that is shaped like an inverted, truncated cone. This partition divides the tank into the two chambers, an outer aeration chamber and an inner clarifier chamber. This design may also incorporate a pyramid shaped deflector placed beneath the truncated conical partition to deflect solids settling out of the clarifier chamber back into the aeration chamber for further bacterial digestion.
Any solids remaining in the wastewater entering the clarifier chamber are expected to be converted by the bacteria in the clarifier chamber before the water reaches the outlet. Since this does not always happen, it is best to minimize the amount of solids reaching the clarifier chamber by efficiently exposing all solids in the aeration chamber to bacterial digestion and avoiding solid accumulation in the form of sludge.
Wastewater treatment plants of all shapes suffer from an accumulation of sludge in the tank. Sludge accumulates due to circulatory “dead spots” in the tank where the fluid does not flow. Dead spots may occur in corners of vessels due to the circulation pattern achieved in the vessel. Dead spots may also occur with the use of diffusers in two or more locations due to the interference pattern produced in the circulation or currents by the diffusers. It has been determined, that sludge tends to accumulate at the base of deflectors and, even worse, directly below the clarifier chamber. As discussed previously, sludge build-up results in the release of nitrogen gas. When the sludge is below the clarifier chamber, the nitrogen bubbles up into the clarifier chamber producing scum and interfering with the operation of the clarifier.
While the use of diffusers in multiple locations necessarily creates the problem of circulatory dead spots where sludge accumulates, this problem is accentuated since air entering into multiple lines is not emitted evenly. The air tends to come out more from one diffuser that the other, particularly if the tank is slightly tilted.
Current U.S. Pat. Nos. 4,664,795 and 4,834,879 by William A. Stegall et al issued May 12, 1987 and May 30, 1989 respectively, disclose the use of a diffuser in the rectangular-shaped treatment plant such that the placement of the diffuser opposite of the baffle and deflector set up a circular pattern in the aeration chamber specifically to avoid the migration of solids into the clarifier chamber. The drop line delivering air to the diffuser is placed directly below the inlet to the wastewater treatment plant and close to the bottom of the plant. The position of the diffuser creates a rolling pattern such that fluid carrying solids moves away from the opening of the clarifier chamber. Sludge build-up in low- or no-circulation zones is not addressed, but the circulation pattern as demonstrated in the drawing, while sweeping the bulk of the fluids into motion, does not sweep into the corners of the chamber. Presumably, this is where sludge build-up occurs.
U.S. Pat. No. 5,266,239 issued to T. Gig Drewery on Nov. 30, 1993, discusses the use of a wastewater treatment plant with an truncated, inverted conical partition having three drop lines for air, as shown in the drawings. The drop lines with diffusers for releasing air are spaced circumferentially and placed near the bottom of the plant. The diffusers create a current including three rolling patterns. The patent drawings show downwardly sweeping necessitated by the interference pattern of the neighboring diffusers. This creates multiple dead zones on the bottom of the aeration chamber. With the use of multiple diffusers, one such dead zone is created directly beneath the clarifier chamber.
U.S. Pat. No. 5,221,470 from the current Applicant, Jerry L. McKinney, issued Jun. 22, 1993, discloses a treatment plant having an inverted truncated conical partition and a pyramidshaped deflector below. One of the inventions of this patent is the use of rigid conduits through which flexible air hoses extend to discharge air adjacent to the bottom of the aeration chamber. These rigid conduits are attached to the plant wall and extend vertically towards the bottom of the plant. The use of two diffusers creates interference patterns similar to those exhibited in the Drewery patent.
It is a feature of this invention to minimize or eliminate sludge build up in a wastewater treatment plant.
It is a further feature of this invention to create an improved current in a wastewater treatment plant that sweeps all solids into circulation to prevent solids from accumulating in a wastewater treatment plant.
It is a further feature of this invention to position an air diffuser in a single location in the aeration chamber of a wastewater treatment plant to create currents in the wastewater in the tank that will maintain all solids in circulation with the wastewater.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification including the attached drawings and appended claims.